The present invention relates to a control method of the auto-balancing system of an optical disk drive and, more particularly, to a control method, which can assist the balancing mass to move smoothly to an opposite position of the unbalance vector of an optical disk during the acceleration process to achieve best balancing effect.
Along with the progress of media-accessing technology of optical information, the reading speed of optical disk drives used as computer peripherals has been continually increased. Nowadays, CD-ROMs with spindle motors having rotation speed exceeding 10000 rounds per minute (RPM) have become the mainstream products in the market.
When the spindle motor rotates at a high speed, the eccentric swinging force resulted from the unbalanced mass of an optical disk will be increased, resulting in problems such as vibration and noise.
In practical applications of optical disk drives, excess vibration will cause the instability of reading capacity of the optical reading head so that optical disk drives can not steadily read data at the highest rotation speed. Additionally, the noise generated by optical disk drives with high rotation speed will cause discomfort and botheration in usage to the user.
Therefore, how to suppress vibration effectively to let optical disk drives read data steadily when optical disks therein rotate at high speeds is a problem that all manufacturers of optical disk drives must overcome.
Conventionally, there are three methods that the manufacturers of optical disk drives adopt to reduce the vibration resulted from the unbalanced mass of optical disks rotating at a high speed: (1). The weight of the reading mechanism is increased directly to reduce the vibration; (2). A dynamic absorber is used to reduce the vibration; (3). An auto-balancing system is used to reduce the vibration.
All the three methods mentioned above can reduce the vibration of optical disk drives. In theory, the effect of the auto-balancing system is best because it directly reduce the exciting force of vibration by means of adding balancing mass.
The auto-balancing system used by the manufacturers of optical disk drives is generally situated above (or below) the spindle motor. The auto-balancing system comprises a balancing mass (generally being a predetermined number of steel beads) and a housing (generally being of circular shape) for bearing the balancing mass. In the rotor dynamics, when the rotation speed of the spindle motor exceeds a critical speed, the position of added mass will be situated at the opposite position of unbalance vector of the original optical disk. Thereby the unbalance of the original optical disk can be counterbalanced, and the vibration of the optical disk drive can be reduced.
However, because of some limitations in manufacturing (e.g., the degree of circularity, the degree of homo-centricity, the surface roughness, and the uncertainty in acceleration which is caused by different rotation load resulted from unequal unbalance of different optical disks during the accelerating process of the spindle motor), the balancing effect in practical applications is not as perfect as that predicted in theory.
Accordingly, the primary object of the present invention is to propose a new control method of the auto-balancing system. The proposed control method can reduce the vibration caused by the unbalance of optical disks through an effective and steady way when the optical disks rotate at a high speed. High-speed and exact reading of data and smooth rotation can thus be achieved.
To achieve the above object, the present invention proposes a control method of the auto-balancing system of an optical disk drive. The present invention adds a procedure of constant rotation speed in the acceleration process of the spindle motor when the rotation speed is below a critical speed. According to the rotor dynamics, when the rotation speed of the spindle motor is below the critical speed, the position of added mass will be situated at a position at the same side of the unbalance vector of the original optical disk. Thereby the balancing mass will remain at the position of worst balancing effect in the procedure of constant rotation speed. After the procedure of constant rotation speed, the spindle motor will be accelerated to pass the critical speed of the system by the largest torque. Because of inertial effect, when the rotation speed of the spindle motor exceeds the critical speed, the balancing mass will leave from the original position of worst balancing effect and smoothly move to an opposite position of the unbalance vector of the original optical disk. Best balancing effect can thus be achieved.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawings, in which: